Implantable medical electronics devices consist of an implanted pulse generator that is used to provide electrical stimulation to certain tissues and an implantable lead or leads that are used to transmit the electrical impulse to the targeted tissues. Examples include cardiac pacemaking, and a number of related applications for cardiac rhythm management, treatments for congestive heart failure, and implanted defibrillators. Other applications for implantable pulse generators include neurostimulation with a wide range of uses such as pain control, nervous tremor mitigation, incontinence treatment, epilepsy seizure reduction, vagus nerve stimulation for clinical depression, and the like.
Despite various suture fixation devices, nerve stimulation leads can be dislodged from the most efficacious location due to stresses placed on the lead by the ambulatory patient. A surgical intervention is then necessary to reposition the electrode and affix the lead. The implantable pulse generator (“IPG”) is programmed to deliver stimulation pulse energy to the electrode providing the optimal nerve response. The efficacy of the selected electrode can fade over time due to dislodgement or other causes.
Physicians spend a great deal of time with the patient under a general anesthetic placing the small size stimulation electrodes relative to the target nerves. The patient is thereby exposed to the additional dangers associated with extended periods of time under a general anesthetic. Movement of the lead, whether over time from suture release or during implantation during suture sleeve installation, is to be avoided. As can be appreciated, unintended movement of any object positioned proximate a nerve may cause unintended nerve damage. Moreover reliable stimulation of a nerve requires consistent nerve response to the electrical stimulation that, in turn, requires consistent presence of the stimulation electrode proximate the target nerve. On the other hand, if the target nerve is too close to the electrode, inflammation or injury to the nerve can result, diminishing efficacy and possibly causing patient discomfort.
Cardiac pacing leads are commonly provided with passive fixation mechanisms that non-invasively engage heart tissue in a heart chamber or cardiac blood vessel or active fixation mechanisms that invasively extend into the myocardium from the endocardium or epicardium. Endocardial pacing leads having pliant tines that provide passive fixation within interstices of trabeculae in the right ventricle and atrial appendage are well known in the art as exemplified by U.S. Pat. Nos. 3,902,501, 3,939,843, 4,033,357, 4,236,529, 4,269,198, 4,301,815, 4,402,328, 4,409,994, and 4,883,070. Such tined leads typically employ tines that extend outwardly and proximally from a band proximal to a distal tip pace/sense electrode and that catch in natural trabecular interstices when the distal tip electrode is advanced into the a trial appendage or the ventricular apex.
Certain spinal cord stimulation leads have been proposed employing tines and/or vanes as stand-offs to urge the stimulation electrode in the epidural space toward the spinal cord as disclosed in U.S. Pat. Nos. 4,590,949 and 4,658,535, for example, and to stabilize the stimulation electrode in the epidural space as disclosed in U.S. Pat. No. 4,414,986, for example.
Stimulation leads for certain pelvic floor disorders have been proposed with a fixation mechanism that includes a plurality of time elements arrayed in a tine element array along a segment of the lead proximal to the stimulation electrode array, such as for example in U.S. Pat. Nos. 6,999,819; 7,330,764; 7,912,555; 8,000,805; and 8,036,756. Each tine element includes a plurality of flexible, pliant, tines. The tines are configured to be folded inward against the lead body when fitted into and constrained by the lumen of an introducer.
Peripheral nerve field stimulation (“PNFS”) involves delivery of stimulation to a specific peripheral nerve via one or more electrodes implanted proximate to or in contact with a peripheral nerve, such as disclosed in U.S. Pat. Publication No. 2009/0281594. PNFS may be used to deliver stimulation to, for example, the vagal nerves, cranial nerves, trigeminal nerves, ulnar nerves, median nerves, radial nerves, tibial nerves, and the common peroneal nerves. When PNFS is delivered to treat pain, one or more electrodes are implanted proximate to or in contact with a specific peripheral nerve that is responsible for the pain sensation.
During the implantation procedure the surgeon selectively activates the electrodes to test nerve response (also referred to as “mapping”) to determine optimal lead position. Fixation structures on the lead are typically restrained by the introducer during the mapping process. Optimal lead placement must be achieved before deploying any fixation structures.
Prior art fixation strategies include barbed or angled structures that provide greater fixation in one direction along the central axis of the lead. For example, U.S. Pat. No. 7,684,873 (Gerber) and U.S. Pat. No. 6,999,819 (Swoyer et al.) both disclose fixation tines angled with respect to the central axis of the lead. This approach tends to provide excess fixation in the proximal direction, complicating lead removal, and inadequate fixation in the distal direction.
The asymmetry in these fixation approaches creates greater risk of the lead being inadvertently displaced in the distal direction, such as by patient movement, rather than in the proximal direction. For example, if the lead is subjected to cyclical push-pull forces, the angled tines provide a ratcheting-action that favors displacement in the distal direction over the proximal direction. Over time, the lead will tend to migrate in the distal direction, resulting in misplacement of the electrodes relative to the target nerve tissue.